#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(LL i = a;i<b; i++)
#define rrep(i,a,b) for(LL i = a;i>=b; i--)
#define INF ((1LL<<62)-(1LL<<31))
#define ooki 9,223,372,036,854,775,807
#define tii -9,223,372,036,854,775,808
typedef long long LL;
int main(){
     vector<int> a(4);
  rep(i,0,4){cin>>a[i];}
  sort(a.begin(),a.end());
  rep(i,0,3){
    if(a[i+1]-a[i]!=1){cout<<"No"<<endl;return 0;}
  }
  cout<<"Yes"<<endl;
}